The wireless network starts at the TBR. It is the border between the Thread wireless and Ethernet network at the Northbound Edge gateway. TBRs change the communication media from wireless to wired but have no gateway functionality.

Typical system topology of a self-healing Thread network

The TBR is connected directly to sleepy end devices (SED) and mesh extenders (TME). TMEs extend the Thread radio range to connect additional TMEs and SEDs located further away from the TBR.

Wireless solution limits

Item

Protocol

System limit
(max. per project)

Thread border router (TBR)

Thread

4 (per edge controller)

Thread mesh extender (TME)

Thread

15 (per network)

Wireless room actuator (WRA)

Thread

20 per TBR/TME
Max. 100 (per network)

Setpoint scheduler

-

10

For further Thread system limits, see KNX IoT Thread System Description, https://siemens.com/bt/download → ID: A6V14455022.

Basic Design Rules

  1. Metal and thick concrete structures significantly reduce Thread wireless signal strength.
  2. Clear lines of sight between devices minimize the damping effect.
  3. Other wireless technologies can cause interference.
  4. Mounting wireless device higher can avoid damping.
  5. Low link quality and low signal strength adversely affect stability and shorten battery life.
  6. Observing all system limits improves operation.
  7. Use off-the-shelf tools to plan, install, test, and troubleshoot wireless systems.

Signal Range

The Thread signal range in buildings is between 15 m and 50 m, depending on the individual building conditions. As a rule of thumb, the Thread radio range between two Thread devices is R = 30 m. The maximum recommended number of hops in a Thread system is 4 so that the maximum recommended number of TMEs between a TBR and an end device is 3.

Maximum number of hops in a Thread system

TBR

SED

Successful hop

Thread link (wireless)

TME

Thread leader

Failed hop

Ethernet link (wired)